Dark coffee with no sugar or cream added is “generally”* alkaline. Coffee with sugar and dairy cream becomes acidic. The sugar and the dairy cream or milk added to the coffee make or turn the coffee acidic.

Dark coffee with no sugar or cream added is described as “generally” alkaline because it seems that only good quality coffee is alkaline. Some cheap coffee brands are acidic. Also, some of the luxury blends or fruit flavored blends of coffee are acidic.